The present invention relates to a nuclear boiler for a pressurized ordinary water reactor.
The invention more specifically relates to a nuclear boiler comprising a vessel sealed in its upper part by a removable cover, a basket-shaped member carrying the reactor core and separating the vessel into a hot inner area and a cold outer area, at least one steam generator positioned within the vessel and comprising a tightly sealed enclosure and a tube plate separating the enclosure into a primary part or water box and a secondary part, the tube plate carrying U-tubes, whose ends issue into a cold area and a hot area of the water box, defined by an inner structure, two linear, coaxial tubes defining an inner pipe and an annular outer pipe respectively connecting the hot areas and cold areas of the vessel and the water box.
Nuclear boilers of this type, which are also called pressurized ordinary water nuclear boilers are described in French Pat. No. EN 74 09517. In such boilers, the vessel is connected to the steam generator by linear, short tubes regrouping in the same envelope the outward and return flows of the primary fluid, i.e. the hot and cold connecting pipes.
If the connecting pipes are fractured, which constitutes one of the most serious accidents to be taken into consideration when designing a nuclear power station, boilers of this type have the advantage of providing a support securing the steam generators, i.e. only permitting a limited and controlled displacement thereof. However, the result obtained as a result of such support is not independent of the shape of the fracture. In other words, it is not possible to limit to a given value the leak caused by fracturing of the connecting pipes by supporting the steam generators.